Thanks for the feedback. The progress bar shows a combination of your progress towards the required warp vector velocity and alignment, or if you are closer to it, the progress towards the 3 min auto-warp timer. What this means is that usually, it will be indicating your ships progress towards the warp vector, but if you get stuck, it will transition to a countdown to the auto-warp.
As others have rightly mentioned, the EVE UI is already very busy, so we were conscious of not adding too much more complexity, while trying to indicate that there are a few factors at play when trying to activate your warp drive. At the very least, we hope that this provides more information than was available before this change.